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- R. Jones, H. Schmickler
CERN, Geneva, Switzerland
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A so-called "Head-Tail" chromaticity measurement system has recently
been installed in the CERN-SPS, which allows the chromaticity (Q’) to be
calculated from several hundred turns of data after transverse
excitation. The measurement relies on the periodic dephasing and
rephasing that occurs between the head and tail of a single bunch for
non-zero chromaticity. By measuring the turnby-turn position data from
two longitudinal positions in a bunch it is possible to extract the
relative dephasing of the head and the tail, and so to determine the
chromaticity. In addition, by changing the orbit of the circulating beam
this technique allows the variation of chromaticity with radial position
(Q’’) to be measured with a much higher resolution than is currently
possible using RF modulation. This paper describes this "Head-Tail"
measurement technique and discusses some recent results obtained using
prototype LHC beam (25 ns spacing) in the CERN-SPS.
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